The engine.git repo doesn't need a copy of the Dart SDK anymore.

Fixes https://github.com/flutter/flutter/issues/2618

When developing the engine from Xcode, it is useful to see log output in Xcode's UI. We were redirecting streams away so that the tools could pick read these logs. With the change to the scheme, when running from Xcode, the logs will show up in Xcode's UI. When, running from the tools, that flag will not be present and the tools will work as they always have.

* Added instrumentation for timings.

* A few more traces for better granularity.

Can happen when calling getWordBoundary on an empty Paragraph.

* Expose a Paragraph.getWordBoundary method to dart.

Used by text selection to select a word.

Earlier, the dynamic service loader was part of the main application
bundle. But now, we package it into Flutter.framework and let the user
control "main". The old path was looking for the manifest in the wrong
spot.

* Updating CONTRIBUTING.md to mention latest paths

* Update CONTRIBUTING.md

create_ios_sdk.py takes additional arguments that specify the out directories of both the device and simulator builds. (#2673)

Was only used by the buildbot to test that the armv7 precompiler paths built. The Android AOTC variants check that now.

This needs to be updated for the latest Mojo APIs

This patch:

 - makes dart traces (coming from the VM and the timeline API)
   available to mojo:tracing
 - adds --vm-complete-timeline parameter, which makes the Dart VM enable all
   categories of timeline traces from the beginning, allowing to do startup
   tracing

This is based on the equivalent support in dart content handler.

Fixes https://github.com/flutter/flutter/issues/3162.

Change the "develop" runtime mode back to "debug" and rename the "debug" build configuration to "unoptimized" (#2669)

We were all set up for this but for some reason we were actually decoding the
images on the main thread.

Fixes #3803

* Wire up accessibility scrolling

flutter/flutter#1664

* Update to mojo 9a791294e429f9f2ca4f427796a284edb6f6768e

* Update to account for Mojo API changes

* Add mojo service for accessing the system clipboard.

Hooked up for iOS and Android.

BUG=https://github.com/flutter/flutter/issues/1567

We no longer provide the main function for Flutter apps on iOS. Instead, we
just provide Flutter.framework, and the end-developer provides main.

Also, remove unused build rules for building Runner.app. We don't build that
target anymore.

flutter/flutter#1664

* Move node implementation to Objective C

This changes AccessibilityBridge::Node (C++) to be AccessibilityNode (objc)
in order to have the nodes returned directly as ui accessibility elements.
This buys us a few things:

1) We can now return an element tree instead of a flat list, thus negating
   the need to maintain a global rect and global translation
2) We use less memory since we don't need to instantiate both nodes and
   their ensuing accessibility elements
3) accessibility elements can now implement the methods necessary to respond
   to events like user scrolling

https://github.com/flutter/flutter/issues/1664

This patch switches us to building Runner.app on the end-developer's machine,
which will eventually let them customize their app.

Hosting this script inside the repo will let us change the contents of the SDK
without having to synchronize a change on the infrastructure and in the repo.

These Dart_GetField calls show up on traces. This patch removes almost all of
them from the Canvas interface. We still have a few in drawAltas and
drawVertices, which will be removed in a later patch.

Fixes https://github.com/flutter/flutter/issues/3256